Are Cast on Spells energy gains handicapped for -Breaches/ Expeditions/ Delirium?

Hey Everyone,

There is a noticeable reduction in the amount of Cast on energy that I gain For breaches, Delirium and Expeditions. I'll clear level 15 maps with a clean and predictable cast rate of my spells. Is there something that I'm missing?

I'm running cast on minion death with an additional boost to energy when I ignite. But even when running max ignite chance and the mobs noticeably on fire, my proc rate is abysmally low.

Do these mobs have some mechanic I'm not aware of that effectively handicaps Cast on builds?

Thank you for the help in advance!

-PapaStonk